The present invention relates to a method for the molding and soldering of electrical connection pads to the electric connection-receiving zones of circuits electronic circuits or components.
The electrical connections of electronic components such as integrated circuits comprising a large number of connection points are usually formed by solder balls soldered to metal connection-receiving zones of the substrate of the component. These connection-receiving zones are located on the face by which the component is attached to an electrical interconnection circuit.
A known method for making electrical connections of an integrated circuit comprises the following main steps: the manufacture of solder balls of the requisite diameter, the dipping of the balls in a flux and the deposition of the balls on the substrate of the component; the passage of the component equipped with balls through a furnace in order to carry out the soldering.
The balls are deposited on the substrate by a suction or screen type device depositing balls on the connection-receiving zones of the component.
These devices are costly and the making of the balls and their storage is very costly.
Another technique consists in making and soldering balls by means of the reflow of solder paste deposited by silk-screen process on the connection-receiving zones of the component. The solder paste is subjected to silk-screen process through two masks superimposed on the substrate. The top mask is used only to deposit the paste. The other mask serves as a mold and remains in position until the reflow of the solder paste in a through furnace. Owing to the presence of the flux, the substrates and the masks have to be cleaned.
Even if the solder paste is three to five times less costly than a prefabricated ball, the need to use these masks means that this technique too is a very costly one.
In order to overcome the drawbacks of the prior art, the invention proposes a method for making balls or solder connection pads on an electrically conductive connection-receiving zone of an electric component, the method comprising an injection of conductive liquid alloy into a guide open at one end placed so as to face the connection receiving zone of the component, wherein the guide is formed by two separable parts, a mold and an injection matrix, the mold and the injection matrix comprising passages, with a narrowing of the guide at the level of the separation of the parts, and the parts of the guide are separated while the alloy is liquid
In the method for making solder connection pads according to the invention, as described hereinafter, the mold is the part in direct contact with the substrate of the component, and the injection matrix is the other part.
In a first variant of the method according to the invention, the mold is removed from the component before the solidification of the alloy. The molten metal present on the connection receiving zone of the component takes the shape of a ball when it cools down.
In another variant of the method, the mold is cooled below the liquidus point of the alloy so that the alloy gets solidified in the mold after the separation of the parts. The mold is separated from the component and, optionally, the alloy is remelted so that it takes the form of a ball.
The invention also relates to a guide for the making of balls or solder connection pads on electrically conductive connection-receiving zones of an electronic component, the guide being designed to contain a conductive liquid alloy and being open at one end, wherein it is formed by two separable parts comprising passages with a narrowing of the guide at the position of the separation of the parts.
In one embodiment of the guide, the two parts are separable in the direction of injection of the liquid alloy in the guide.